Absorption separation process for hydrocarbons



J-uly 25, 1950 P. H. DEMING 2,516,507

' ABsoRPTIoN SEPARATION PRocEss FOR HYDRQcARBoNs Filed March 29, 1947 Patented July 25, 1950 ABSORPTION SEPARATION PROCESS FOR 'IIYDROCARBONS Philip H. Deming, San FranciscojCalif.,assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application March29, 194..7, s-SerialNo.. 738,177

This invention relates to a process for the separation of lower molecular weight hydrocarbons, and more particularly to an improved absorption separation process for the separation of ,a given hydrocarbon component from gaseous admixture thereof with both more and less volatile `hydrocarbons.

It is conventional to separate a mixture of lower molecular weight hydrocarbons, such4 as a mixture of Ci-C4 car-bon-atoms-per-molecule hydrocarbons, including saturated and unsaturated hydrocarbons, into desired fractions by conventional fractional distillation processes by eiecting the fractionation in a suitable fractionating column under sufficiently low temperatures and/or under superatmospheric pressures so as to obtain adequate rectification in .the fractionator.

It is also known to effect separation of .a mixture of gaseous hydrocarbons into at vlea-st two fractions by a process wherein the gaseous mixlture is `contacted with a counterflowing liquid absorbing medium or a iiuidized :solid adsorbent or it ispassed through a stationary solid adsorbent mass with absorption or adsorption, respectively, of certain oi the mixture components and separation thereof from the non-absorbed or -nonadsorbed components. It is known, for example, to effect a partial separation of Ci and Cz-hydrocarbons from admixture thereof with Ca, with or without higher hydrocarbons by countercurrently lcontactingthe mixture with a. hydrocarbon oil in proportions. and under conditions to dissolve or absorb and remove at least substantially all oi the Ca-hydrocarbons, and thus also the higher hydrocarbons, in the oil. The resulting. raiiinate of unabsorbed C1 and C2 hydrocarbons is used for many purposes, .such `as for fuel purposes, recycling to gas-distillate wells, and a source of ethylene and ethane for conversion into valuable chemicals such as ethanol, ethyl chloride, ethylene glycol, etc. However, in the use as a basic chemical for chemical synthesis, it is necessary to eiiect a separation ofy the C2 hydrocarbons, particularly ethylene, from the methane, which separation requires additional operations, gas handling processes, equipment, and the like, all oi which increase the cost of preparing the ethylene in a suitable concentration and purity. Y

It is an object, therefore, of this invention to provide an improved method for the separation and recovery of Cz-hydrocarbons from admixtures thereof With C1 and Ca hydrocarbons. ,A further object is to provide a method which effects more complete recovery of C2 hydrocar- 9 clams. (o1. iss-7115i bons from a mixture of C1-Ca' hydrocarbons in single contacting operation. Another object is to provide a lprocess .for .the separation of C2 hy-y drocarbons from gaseous admixture with C1 and Cs hydrocarbons yand .which process utilizes en- .tropy Achange of mixing oi an absorption oil with the C3 hydrocarbons to effect stripping of dissolved C2 hydrocarbons'therefrom. A. still further object is to provide an improved absorption yprocess for the separation of a given hydrocarbon from admixture with hydrocarbons some of which are more readily and some less readily absorbed lor dissolved in a given absorption medium than the given hydrocarbon. Other ob- .jects .and advantages .of the present invention will Vbe evident from theY following detailed .desciption of theinvention.

Now, in yaccordance with the present invention, an'improved process has been provided "for the lseparation of a given hydrocarbon from gaseous ,admixture thereof with hydrocarbons some of which are more readily ,and some less readily absorbed or dissolved in -a given .absorption. medium than the given hydrocarbon, which process the gaseous admixture is countercurrently contacted in a contacting zonewitha given body of a iiuid adsorption medium .selected to eiiect only substantially ,complete absorption oi said more readily absorbed hydrocarbon, and a' gaseous fraction of unabsorbed material withdrawn `from the contacting zone at an intermediate point thereof which is substantially free,

of said more readily absorbed hydrocarbon .and at which point withdrawal of a .substantial fraction` of, the unabsorbed materiall in the gaseous state can be made and in which substantial frac- .tionalone .the content of said given hydrocarbon is substantially equivalent to, .and the content of the less readily absorbed hydrocarbon is .substantially vless than, their contents, respectively, of the separated gaseous fraction all of the unabsorbed gases were withdrawn at that pointI i.. e. of the original unabsorbed gas. y f

,Descrbedgeneralln the process, as applied. .to an exemplary mixture'of three gaseous hydrocarbons A, B and .C, where A. B and C, have similar physical properties which Vary more or less progressively in. degree, B .having a given solubility relationship with respect to a hydrocarbon oil absorbent, A being ,relatively more readily yabsorbed or dissolvedv than B in said oil', and C being relatively less readily absorbed than Bin said oil, comprises countercurrently'contacting ,said mixture and a hydrocarbon oil vrabsorbent therefor .in a ycontacting zone while substantially continuously feeding a stream .ofsaid `mixmixture to a section or point in the overall contacting zone intermediate said mixture and said" f" absorbent feed points, and withdrawing from said contacting zone at a point substantially immediately outside said lli-absorptionl section in the direction of flow of the gaseous mixture a substantial proportion of the unabsorbed gaseous v mixture in an amount which has a content of B-component substantially equivalent'r to the total B-component content of the unabsorbed gaseous mixture at that point but with a substantially smaller content of VC-cornponent than the total C-component content of the unabsorbed gaseous mixture `at that point, and passing the remaining unabsorbed gaseous'mixture, through the remaining sectionf (secondary absorption zone) of said contacting zone in countercurrent contact with said 'oil stream, whereby the B-component content of saidreniainingf gaseous mixture is absorbed in said oil and returned therein to said A-absorptionisection wherein it is stripped from the oil byas yet unabsorbed A- component in a followingportion of the gaseous mixture stream and thereby recovered to the withdrawal point vof said `Bcomponent hydrocarbon. s f

Described more specifically, with reference to recovery of Cz-components4 from an exemplary gaseous mixture consisting essentially of methanc, Cz-hydrocarbons (ethane and ethylene) and propane, using as absorbent,`for example, a Cs-Cw hydrocarbon oil, the process comprises' passing the gaseous mixture upwardly in countercurrent contact with a downwardlyA flowing body of the absorption oil, the ratio of :oil-to-gas. rates and amounts being so selected, as determined by experiment or by calculation, based upon known factors such as rate of solution' etc., las to effect substantially complete removal of the propane from the gas stream in alower section (propane absorption section) of the contacting zone, withdrawing a portion (usually a major portion but preferably not over about 80 per cent) of the unabsorbed gaseous mixture containing C1 and C2 hydrocarbons, and which is substantially free of propane, from the contacting zone substantially substances, the only requirement being that the substances are vaporizable and that, what may be called an intermediate substance, or group oi substances, is present with at least two other substances or groups of substances one of which fis 'above' and the other ,below the intermediate substance' with respect toV ease or rate oi being dissolved in or absorbed by a common solvent for vthe three substances without permanent change of said substances. Thus, the invention may be .applied to the separation of various mixtures of hydrocarbon substances which differ in solub'ilities in given common solvents therefor only to a` relatively small extent. Of course, if the solubilities diier considerably, then separation is 4acconn'ilished by well known simple processes of solvent extraction. Mixtures of other organic substances, such as mixtures of alcohols, of acids, of aldehydes, of ketones, of halogenated hydrocarbons, etc., which mixtures may be readily vaporized, may be separated by practice of the invention using various common solvents which normally, under the conditions of the process, exert only a physical or reversible chemical action on the substances. For example, as applied to the separation of a mixture of close boiling, volatile, chloroalkanes, and therefore-a mixture which is diil'icultlyseparable by ordinary distillation, as common solvent to be used in the modied type of rectified absorption of this invention, there may be utilized a relatively higher boiling chloroalkane. Gaseous mixtures 0f two or more a1- kenes and alkadienes with at least one alkane or another alkene or alkadiene may be separated inaccordance with the invention wherein the common solvent used for at least two of the substances may eiect a reversible chemical combina- A tion therewith, such as an ammoniacal copper immediately above the propane-absorption zone to reduce the total volumeA of unabsorbed gases, which reduced volume then is countercurrently contacted with the absorption oil in an upper, B- absorption, section of the contacting zone, the reduced volume being selected to ensure substantially complete absorption of the Cz-content thereof in said absorption oil in said B-absorption section to return the B-content of thereduced volume of unabsorbedV gases to the point of withdrawal of Cz-gasesbyway of'a stripping action effected by as yet"unabsorbed propane in the propane absorption zone, and iinally withdrawing a substantial portion ofv the methane from the top of thecontacting zone, the Cz-'content of the gaseous mixture withdrawn from the intermediate'section of the contacting zone being l salt solution, or the like.

As already indicated, the solvent or absorption medium should be chemically inert toward the substances of the mixture to be separated or, as stated, should not react therewith except Yfor the formation of reversible addition compounds. The ratio of solvent or absorption medium to gaseous Imixture may vary over a considerable range -just so long as the ratio is correlated to other variable factors, such as temperature, pressure, length of primary absorption zone, etc., to ensure substantially complete absorption only of the most readily absorbed substances in the absorption medium in the primary absorption zone. Itwill be understood that for a given mixture of substances to be treated, the ratio of solventtof-mixture, to satisfy the above conditions, will depend on the nature ofthe particular solvent selected for the process.

The separation process of this invention may be practiced under various temperature and pressure conditions, the selected values of each being determined byl each particular case. Thus, in the separation of (J2-hydrocarbons from admixture with methane and propane, utilizing a Cs-Cv hydrocarbon oil as absorption medium, the process may be advantageously carried out at F. and under a pressure of 300 pounds per square inch absolute (psia). With substances which are normally liquid, the process should be carried out at a temperature at which the mixture to be separated will be principally in the gaseous orvapor state, i. e., at a temperature above the' bubble temperature of the mixture, which temperature, of course, will depend on the'p'ressure in the system, which pressure'may be atmospheric, subatmospheric or superatmospheric.

The method of practicing the intention will; be more fully understood from the. following descrip? tion of exemplary embodiments, "thereof taken with reference to the accompanying drawing which is made a part of the speoication, where. in Fig. I is a schematic diagram showing. an proved method for the. recovery of C2 hydrocarbons from. a gaseous admixture thereof. withv- Ci and. Ca. hydrocarbons and Fig. II is. a, Schematic diagram illustrating a multiple separation of a, gaseous mixture containing atleast four carri,-l ponents for which separationsone from. theotl-iers. sdesred.

Referring to Fig. I, I. I. represents, a. contactingy column or tower, represented as a bubble-cap time oi towerfor purposes of; illustration pros vided with top and bottom outlet lines. t2 andV i4, respectively, upper and lower feed. lines, tittand i6.. respectively, a withdrawalline lili interino.,- diate the. points of. communication ofi the feed lines l5.. and. I6 with the column Irl and alsoposi.- tioned to. withdraw gaseous material from be.- tween two consecutive plates inthe column. and positioned. to divide the column H. hypothetically into, a lower or primary absorption or contacting nella and an, upper or secondaryl co ritactine,` Zone; and a. suitableA heating. means t9. disposedin the lower part of the column.,

In operation, a mixture of;` Q1, Ca and; Ca` hydrocarbons is delivered; through lineI I6, toco1- t I.- and a suitable liquid absorption oil, e. e. a. mixture of Cit-Cn hydrocarbons. is deliycred thereto through line l5` and the C1. Ga and Cs gaseous mixture is contacted as it iiows. upwardly through. column; Il4 with. the downwardly flows ine. absorption. oil.. The ratio or the ratesoi; now of the .materials thus. contacted in passing through the column is adi-ustedvso that .sub-.- stantialiy all of the Cs-hydrocarloon component is. absorbed; in the absorption oil. within the primary contacting zone below the exit of line Thus, a, iiow.- control. 20.4v in line, I5; may: be used; tol control' valve 2d in lince. Il. Eitherthe ratio of rates. of flow.` oi" the materials is. so ad: justed and/or, if. preferred or; desirable, an amount of. heat energy is supplied to the ppi.- mary absorption zone by means ofany suitable heating orreboiler means i9 to. drive: or Strip from, thel absorption oil when itis in` the'prmany. absorption zone. mostr all. of f any.- dissolved Qr ab.- sorbed C2 hydrocarbons.

The fat oil containing the Cs-hydrocarbons as formedi in the. primary absorption. zone is Withdrawn, from the lbottom of column Hr through line is, which is provided withA control valve: 2:2 which controls the rate ofv flow .Ofc oil there."` through.y responsive to variations in, the liquidv level in thebottom of column I-.I, control; being made. by means of. a liquid level control 2,4.; A pump 2.5 in line i4: pumps the fatoilto an upper section of aV stripping column. 2.o which is pro.- cided. with a suitable heating means. 151; in: the bottom` thereof.` The fat. oil is stripped irl-,column 2E substantially free of; the absorbed C :t hydro: oarbons which are discharged through; valued line 2.9, and the resultinglean oiliis'returnediby means of line 3.0, pump 3.1, controlrvalve. 32. and. line. 3.3 hach* to line 1:5; and; therethrough; to. abs Sorption column: H. Valve 3.2.. isf controlled. by means of. a. liquidi level responsive control des vice; 34..

Substantially all of the Cs. hydrocarhonzcone tent-Qithe gaseous. iced. stream; haying,Y beenA ah serbed in. the absorption oil.; inf. the-.- primary abs notation acne below.l withdrawal. line ti'.,t:he. ra-V unabsorbed portion of. the. gaseous. ture containing the.. C1- and, C2. hydrocarbons thereof lis now divided into two separate trace tions. the.y one being withdrawn through. valved line k1 and the other fraction. being: contacted i-n the secondary absorption zone above the with..- drawal point; oi the. line. tl with the. iresh .abe sorption; oil.. With the removal of; a portion. ci the,l Cit-.Gs gaseous mixture, through line Il,vv the rate, of' eas Elow through the. secondary Aabsorption zone isY materially reduced fromwhat` the rate would be without. such withdrawal. By ludieionsly adjusting; the proportion of the. Ci-C'z gaseous'. mixture wftlrdrawn in line.` l1, the con? tacting' conditions.. particularly the relativer-.aies oiiow ofi eas. and. oil, in the secondary Zone can he adjusted; to insure substantially complete ab sorpt-ionin. the oil; ofi the (3a-content. of saidother fraction of sas passing into the secondaiwA ab? sorption zone., This absorbed Cafcontent; then is; returned in the. oilv to. the.v primary zone wherein it; is` stripped therefrom some.` ofthe f2s-con: tent. of a. following portion or the gas stream, and thereby enriches the. unalosorbed C2i-C2. gas.- mixatures. In this manner, it is seen that., in effect, the entropy change of. mixing the oil. and the; Ca hydrocarbons is' utilized in. effectingV theI separa-E tion. .or Q1. and C2i. hydrocarbons inthe secondary absorption zone.

- The unabsorbed. gas: content; of the eas-.- passed intoi the.; secondaryy absorption zone. is; discharged therefrom through` line |25, the discharged'. eas hein-g substantially Giehydrocarbons..

Thus. the C2containingy eas withdrawn through: line; It is richer with respect. to Ca-hys droearbons. by aVA value corresponding to the; dis.- charee of. lion-3a` material inline |,2,y since, with,- outl such separation and discharge all of thefCihydrocapbons; wouldl be associated with the G2 hydrocarbons in; the Withdrawn C22-hydrocarbon stream, This: decrease in the amount of C11l in the Gafstream materially reduces equipment-prequirements for further handling of' the C2- strearn-,Vs thel economies` thus realized being ob vtained at thev expense oi"l otherwise lost entropy change resulting from the mixing (dissolving), of. the Cs in theoil.

It.. will be` understood that the present invention as illustrated in Fig. I may be` appliedA to, the case where a. multiplicity of separations is desired. Fig; Il illustnates` an'. application; of the invention,I toj separation of a wet hydrocarbon gas mixture into several` concentratey fractions. Referring to. Fig.. II, awet hydrocarbon-.gas feed,

Y asmay be obtained fromv awet gas well,y or as,

prising C'1-C4 hydrocarbons together with Ns and/or Ha is delivered through a line 4I to a lower part of a contacting column 42 wherein it is countercurrently contacted with a downwardly flowing body of a liquid hydrocarbon absorption oil, fed to the column through a line 44. The rate otfieedingv the lean oilto the column is adjusted, in View ofthe composition of the feed, the natureof the feed oil, and. the temperature and pressure. maintained. inthe column, so that-sub,- stantially all. of the. C3 material will be absorbed by the oil While in the indicatedv C3 absorption zoneV (primary), that is, at least by the time the C3 material in the gas feed reaches the level of the'. gaseous take-.offV line 45. A substantial proportion; of the gas. atv the level of take-off line is withdrawn through .line 45 as a C'2-concentrata` thev proportion withdrawn being selected sd that` as the remaining gas contacts the oilln 'a5-raso? the-C2 or secondary absorption zone, on account of the reduced gas flow rate, substantially all of the C2 content thereof is absorbed in the oil, therebyv being returned to the Ca absorption zone from which it is stripped by means of as yet unabsorbed Catherein. By this manner substantially all of the C2 hydrocarbon contentof the 'feed gas is .separated in line 45, being mixed,.of course, with some but not all of the lighter' components. The same type of operation is repeated at the `point in the column level with withdrawal line 46 and as correlated with vabsorption of C1 inthe C1 or tertiary adsorption zone, returning it to the secondary absorption zone, displacing it therefrom by as yet unabsor-bed C2 material and thereby enriching the gaseous material immediately above the C2 absorption zone 'with respect to C1 material, aC1 concentrateV being Withdrawn through line 4B. The unabsorbedv N2 and/or H2 is discharged through exit line 41. A suitable heating means 49 in the bottom of the column may be utilized to aid in the rectified absorption and/ or to adjust the upper boundaries of therespective absorption zones, as will be readily understood. Also, auxiliary heating and/oi' cooling means may be provided in any or all of the separate contacting zones. Fat oil containing absorbed C3 and heavier hydrocarbons is withdrawn through line 50. 'As an illustration of the utility and advantage of separating a wet hydrocarbon mixture. by practicing the present invention, when applying the inventionv to a separation as illustrated in Fig. II, an excess of about 40% of fractions lighter than ethylene can be rejected upwards through the column above the C2 absorption zone with a corresponding enrichment in its C2 con'- tent of the Withdrawn C2 concentrate streamby approximately 40% of its' original concentration. Further, approximately 25% of the rejectedlight fraction can be still further treated to reject above the C1 absorption zone the N2 and/or H2 content thereof, thus enriching the C1 concentrate which is Withdrawn through line 45.

i To illustrate further the utility and advantages ofthe invention, there is given in the table comparative material balances resulting from treatinga Wet hydrocarbon gas feed of the naturedescribed above with reference to Fig. II, in one casein a single contacting zone with :absorption and separation only of the C3 and heavier components of the gas'feed, land in anothercase according to the practice of the invention as described With reference to Fig. II, except for the omission of the precontacting in C1 absorption Zn.' l

` TABLE Material balance Only C2 Absorp- C and C3 Abtion Zone sorption Zones Methane reected None 1.5 MHSCF/day. 0% 35%. Ethylene Loss None 1.5%. Ethane Loss o 0.2%. Glas Rate to Ethylene Re- 6.4 M2SCF/day 4.9 MBSCF/day. .icovery from Ethane. i.

j M01 Moi a. Compositmn of Gas to Ethyl- O1: 68 C1: 57.9 ene Recovery. C2 8.2 C2 10.7 C| 23.1 Ci; 30.5 Cf 0.7 Ca- -0.9

f '.'It is readilyseen that since 68% ofv 6.4 (435-) MZSCF/day is-considerably more than 57.9% of 4.9 (2.84) M2SCF/day, then there is a reduction of about 1.52 kM2SCF/day (about 25%) in the amount of methane that is carried to the ethyl.- ene-ethane fractionating equipment. Furthermore, in addition to representing a saving in subsequent separation, this reduction in volume representsa saving in pumping requirements, compressors,etc. It is also seen that the 4.9 M2SCF/ dayof gas having a C2 content of 41.2% (2.02 -M2SCF/day) contains substantially the same amount (2.00 M2SCF/ day) as the 6.4 M2SCF/ day of `gas having a C2 content of 31.3%.

a. vAlthough the embodiments of the invention as represented byFigs. I and II are practiced in fa single contacting column divided by the product withdrawallines into two (Fig. I) and three (Fig. II) absorption zones, respectively, it will be understood that the different absorption zones may be within separate columns. Also, and particularly in the case of using separate columns for the different absorption zones, the columns may be of any of the usual types adapted for eiecting intimate contacting between counterowing gaseous material and an absorbent medium therefor. Thus, one or more of the columns may be simply packed columns and the various columns may be of dierent types. l

I claim as my invention: y 1. A process for separating a gaseous mixture consisting essentially of C1, C2 and C3 hydrocarbons, comprising the steps of: passing said gas'- eous mixture in counterowing contact with a liquid hydrocarbon absorption oil forsaid hydrocarbons in a primary contacting zone to absorb thereby a majorproportion of said C3 hydrocarbons and to'strip from said absorption oil the C2 hydrocarbons absorbed thereby in a previous contactingv step as described below; separating the resulting fat absorption oil from primary unabsorbed gases; passing a portion from about 20% to about 50% of said separated unabsorbed gases into counterflowing contact with a lean absorption oil in a secondary contacting zone to absorb thereby the C2 hydrocarbons from said portion of unabsorbed gases to produce the absorption oil for the primary contacting zone; separatingthe resulting absorption oil with the C2 hydrocarbons Vthus absorbed thereby from secondary unabsorbed gases; and passing the absorption oil containing absorbed C2 hydrocarbons from said 'secondary contacting zone into said primary contacting zone for contacting a further portion of said gaseous mixture the flow of absorbent passed through said zones being selected to be approximately the minimum amount required to absorb all of the Cs-hydrocarbons from the gaseous-mixture in the primary zone and the portion of unabsorbed gases passing to the secondary zone being selected to contain approximately the maximum content of Cz-hydrocarbons which may be absorbed therefrom by the absorbent` owing through the secondary zone.

2. A processfor separating a gaseous mixture consisting essentially of C1, C2 and C3 hydrocarbons, comprising the steps of: passing said 'gaseous mixture in counteriiowing contact with a liduid'hydrocarbon absorption oil in a primary contacting zone 'to absorb therein substantially all of said Ca hydrocarbons and to strip from said-absorption oil the C2 hydrocarbons absorbed therein `in a previous contacting step as described below; separating the resulting fat absorption oil from primaryiunabsorbed gases; passing -aminor armaron but substantial portionof said separated unabsorbed gases intor counte'riiowingA contact with a leanv liquidi' hydrocarbon absorption oil in aseoondary' contacting zone to absorb therein. the C2 hydrocarbons from said minor' portion. oi unabsorbed gases to produce the absorption oil for the primary contacting zone; separating the resulting absorption oil with! the Cz'hydrocarbons thus absorbed therein from secondary unabsorbed gases; and passing the absorption oil containing absorbed Cz hydrocarbons from said secondary contacting zone into said. primary vcontacting zone for contacting a further portion of saidy gaseous mixture. f Y 3f. Aprocessv for separating a vaporizable mixture of hydrocarbons consistingl essentially of components A, B and C which decrease inthe order named in their readiness for being -absorbed by a common liquid hydrocarbon absorption oil, which process comprises the steps of: passing a mixture of. said A,v Bl andy Cf hydrocarbons in the vaporstate in counterilowing contact with a liquid' hydrocarbon absorption oil thereforv ina primaryr contacting zone toabsorb therein substantially all. of said A hydrocarbons and' to strip from said absorption oil B hydrocarbonsabsorbedL thereby in a previous contacting step as describedl below; separating the resulting fat absorption oil from the primary unabsorbed vapor; passing a minor but substantial portion of said separated vapor into counterlowing` contact with a lean absorption oil in a secondary contacting zonev to absorb thereby the B hydrocarbons in said minor portion of unabsorbed vapor to produce the absorption oil for the primary contacting zone; separating the resulting absorption oilA with .the B hydrocarbons thus absorbed thereby from` the secondary unabsorbed Vapor; and passing' the absorption oil containing absorbed By hydrocarbons from said secondary contacting zone into said primary contacting zone for con'-l tacting a further portion of said Vapor mixture of A, B and C hydrocarbons.

4. A process for separating a gaseous mixture consisting essentially of A, B. and C hydrocarbons which decrease in the order named in their readiness for being absorbedby a common. liquid hydrocarbon absorption oil therefor, which process comprises the steps of: contacting a gaseous stream of said A, B and C hydrocarbons successi-Vely i-n a firs-t and a second contacting zone Witha counterfiowing stream of a liquid hydrocarbon absorption oil therefor; separating from the rst contacting zone a fat absorption oil which contains substantially all of said A hydrocarbons and a primary unabsorbed gas stream which contains substantially all of said B and C hydrocarbons; separating the primary unabsorbed gas stream into a minor portion containing from about to about 50% of said primary unabsorbed gas stream and :a maior portion of from about 50% to about 80% of said primary unabsorbed gas stream, the major portion of which is Withdrawn as B hydrocarboncontaining product and the minor portion of which is passed to the second contacting zone; separating from the second contacting zone said absorption oil enriched in said B hydrocarbons and a secondary unabsorbed gas stream which is substantially free of B hydrocarbons and contains the C hydrocarbons from said minor portion of said primary unabsorbed gas stream; and passing said absorption oil enriched in B hydrocarbons to said rst contacting zone.

5. A process for the separation of a ,mixture of a plurality' of hydrocarbons A, B, C and D which decrease in the order named in their readiness for being absorbed by a common liquid hydrocarbon absorption oil,. comprising the ste-ps of: contacting a gaseous stream of said A, B', C and D hydrocarbons successively in a series of first, second and third contacting zones with a counterowing stream of a liquid hydrocarbon absorption oil therfor; separating from the rst corrtacting zone a fat absorption oil which containssubstantially all' of said A hydrocarbons and a primary unabsorbed' gas stream Which contains substantially alliv or said. B, C and D hydrocarbons; 'separating the primary unabsorbed gas stream intov minor and major. portions, the major portion of which isY Withdrawn as B hydrocarboncontaining rproduct and the minor portion of which is passed to they second contacting zone; separating vfrom the; second contacting zone said absorbent enriched in said B' hydrocarbons andy a. secondary'unabsorbed vgas streamY which isl sub:-I stantially tree of B hydrocarbons and contains the C and D hydrocarbons from said minor portion of said primary vunabsorbed gas stream ;l passing said, absorption oil enriched in B hydrom carbons; tosaid' first contacting Zone; separating: the secondary unabsorbedzgas stream into minor and major portions, the major portion of Whielr is `Withdrawn as C hydrocarbon-containing prod... uctA and the minor portionl of Which, is passed to the third' contacting zone; separating Afrom. the third contacting ZoneV said absorption oil' enriched in said C hydrocarbons and a tertiary unab-l sorbed gas stream which is substantially'free; of: C hydrocarbons and contains the D; hydrocarbons from said minorl portion Lof said secondary: unabsorbed gas stream; and passing said absorption oil enriched in C hydrocarbons to said second contacting Zone. 1

'6. -A process. for separating a lvaporizable mixture consisting-essentially of chemically related organic compoundsA, Brand' C` which decrease in. the order named `in their` readiness. for being reversibly absorbed by'a'. common liquid absorption medium therefonwhich process comprises; the steps of: 'passing `said mixturein the. vapor state in counterflowing contact with said liquidy absorptionfmedium for said compounds A,l B and C in a primary contacting zone to absorb thereby a major proportion of said A compounds and .tostrip from said liquid :absorption medium the B compounds absorbedthereby in a previous con.-

tacting step as described below; separating the.l

resulting fat absorption medium from primary unabsorbed gases; passingv ai portion of from; about 20%2to about 50% of said separated unabsorbed gases into counterowing contact with a lean absorption medium of said liquid absorption medium in a secondary contacting Zone to absorb thereby the B compounds from said portion of unabsorbed gases to produce the absorption medium with the B compounds thus absorbed thereby from secondary unabsorbed gases; and passing the liquid absorption medium containing absorbed B compounds from said secondary contacting zone into said primary contacting Zone for contacting a further portion of said gaseous mixture.

7. A process for separating a gaseous mixture consisting essentially of C1, C2 and C3 hydrocarbons, comprising the steps of: passing said gaseous mixture through a primary contacting zone in counter-flowing contact with a hydrocarbon absorption oil for said hydrocarbons and containing -as absorbate a substantial portion of C:

hydrocarbons derived as described hereinafter, in relative contacting proportions selected to absorb substantially all of the Ca-hydrocarbon content of said mixture and not more than a minor'content of lower molecular weight hydrocarbons in said oil whereby substantially all of the Ca-hydrocarbon content is removed from said primary Zone as absorbate with said oil and the Ciand Cz-hydrocarbon content of said mixture and said Cz absorbate is removed from the primary zone as unabsorbed gaseous mixture; dividing said unabsorbed gaseous mixture into a product portion and into a second gaseous portion, which second portion is selected to contain substantially the maximum Cz-hydrocarbon content which is removable therefrom by counterflowing contact with the fresh absorption oil recoverable from the oil containing Ca-hydrocarbon absorbate removed from the primary Zone; countercurrently contacting said second gaseous portion in a second contacting Zone with fresh absorption oil in amount corresponding to the amount of oil passing through said primary zone, whereby the C2- hydrocarbon content of said second portion is removed as absorbate with said absorption oil from said second contacting zone; and utilizing' said absorption oil containing said Cz-hydrocarbon absorbate as the absorption oil in said primary contacting zone.

8. A process for separating a, wet hydrocarbon gaseous mixture comprising C1-C4 hydrocarbons and containing C1 and C2 hydrocarbons in a mol ratio of approximately two to one of Ci/Cz, comprising the steps of: passing said gaseous mixture through a, primary contacting Zone in counteriiowng contact with a hydrocarbon absorption oil for said hydrocarbons and containing as absorbate therein a substantial portion of Cz-hydrocarbons derived as described hereinafter, in relative contacting proportions selected to absorb substantially alll of the Csand higher hydrocarbon content of saidmixture and not more than a minor content of lower molecular weight hydrocarbons in said oil, whereby substantially all of the C3- and higher hydrocarbon content is reportion in a, second cointacting zone with ap proximately the minimum proportion of fresh absorption oil to absorb substantially all of the Cz-hydrocarbon content from said second gaseous portion, whereby the (iz-hydrocarbonv content thereof is removed as absorbate with said oil from said second contacting zone; and utilizing said oil containing said Cz-hydrocarbon absorbate -as the absorption oil in said primary contacting zone.

9. A process for separating a gaseous mixture consisting essentially of substances A, B and C which decrease in the order named in their readiness for being reversibly absorbed by a common liquid absorption medium therefor and which are relatively inert toward each other under the conditions of the process, which process comprises the steps of: passing said mixtureY in the gaseous state in counteriiowing contact with said liquid absorption medium for said substances A, B and C in a primary contacting zone to absorb thereby a major proportion of said A substance and to strip from said liquid absorption medium the portion B substance absorbed thereby in a previous contacting step as described below; separating the resulting fat ab'- sorption medium from primary unabsorbedk gases; passing :a portion of from about 20% to about of said separated unabsorbed gases into counteriiowing contact with a lean absorption medium of said liquid absorption medium in a secondary contacting zone to absorb thereby the B substance from said portion of unabsorbed gases to produce the absorption medium with the B substance thus absorbed thereby from secondary unabsorbed gases; and passing the liquid absorption medium containing absorbed B substance from said secondary contacting zone into said primary contacting zone for contacting a further portion of said gaseous mixture. PHILIP H. DEMING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,422,007 Soddy July 4, 1922 2,038,314 Ragatz Apr. 2l, 1936 2,160,163 Nichols May 30, 1939 2,270,903 Rudbach Jan. 27, 1942 2,318,752 Carney May l1, 19431 2,335,009 Holloway Nov. 23, 1943 2,495,842 Gilliland Jan. 31, 1950 

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